How To Launch the Dialer to Initiate Phone Calls:

Use
an Intent action to start a dialer activity; you should specify the
number to dial using the tel: schema as the data component of the
Intent.

Use the Intent.ACTION_DIAL Activity action to launch a dialer rather than dial the number immediately.
This action starts a dialer Activity, passing in the specified number but allowing the dialer application
to manage the call initialization (the default dialer asks the user to explicitly initiate the call). This
action doesn’t require any permissions and is the standard way applications should initiate calls.